My water pipes sing at some low frequency when I shut off the shower, and I have to partially leave the cold water running for a few minutes to stop the noise. The problem seems to be getting worse and yesterday the pipes sang for a few seconds with just the cold water turned on and off. I have 15 year old hot water heater I thought might be the problem, but if it happens with only cold water, I don't see the connection. I can't find any leaks, but occasionally I get a little burst of air from one of the hot water taps after the water has been shut off for several hours. Do I need new pipes?
-Bill